"Jaffar Express train, which was coming from Peshawar, derailed after the train's driver applied emergency brakes when he observed the track bent near Aiman Abada, Gujranwala some 80km from Lahore," a Railways spokesman said.
The Railway authorities did not rule out a sabotage in the derailment.
"Possibility of terrorism can not be ruled out in this case," the spokesman said, adding the authorities would also carry out technical review of the incident with a possibility that the track might have been tampered by someone.
Army troops arrived at the site of the accident to assist civil administration in rescue efforts, Inter-Services Public Relations said.
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The rescue teams shifted the injured to a local hospital.
The condition of three passengers is stated to be critical. Passengers were pulled out of the bogies with the help of ladders.
A relief train was also sent to Gujranwala to bring the passengers to Lahore.
Federal Railways Minister Khawaja Saad Rafique ordered the Railways authorities to directly supervise the rescue and relief activities.
He said the detailed report involving all aspects, including track tampering, would be presented in 72 hours.
Meanwhile, the Railways authorities have changed the routes of three trains including Green Line Up and Down and Tezgam Up following the incident.